On Tue, 2007-05-29 at 14:50 +0200, Willem Vervuurt wrote:

> I am trying to build an algorithm that transforms pictures (all taken
> from the same viewpoint) into their corrected-for-perspective
> equivalents.
> In the GIMP, I can apply the desired perspective transformation to an
> image and retrieve the required transform matrix (it is {{0.485,
> -0.374, 178}, {0, 0.45, 0}, {0, 0, 1}}, reading rows). (See
> http://www.rodo.nl/input.jpg and http://www.rodo.nl/result.jpg for
> input image & desired output, respectively).

I think you are making the wrong assumption that the perspective
transform tool would apply an affine transformation which can be
expressed as a 3x3 matrix. You probably know these matrices for example
from SVG files. The transformation performed by the Perspective
transform tool is however not necessarily an affine transformation. It
uses a 4x4 matrix. Only the upper left 3x3 submatrix 3x3 is displayed
because the other values are always 0.0 or 1.0.


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